Copolymers of propylene with other alpha-olefins, such as ethylene, are well-known and have a wide variety of commercial applications, either alone or when blended with other polymers. Typically such propylene copolymers are produced by a single or multi-stage polymerization process using a catalyst including an activator or co-catalyst that operates in conjunction with a catalyst precursor in the formation of a transition metal complex. This applies to conventional Ziegler Natta type catalyst systems, such as those employing titanium chloride based transition metal catalysts, as well as to the more recently developed single site based catalyst systems, such as those employing complexes with cyclopentadienyl or hetero-atom containing ancillary ligand systems. An activator may also affect the molecular weight, degree of branching, comonomer content and other properties of the resultant copolymer. Typical activators include, for example, alumoxanes, aluminum alkyls and non- or weakly coordinating ionizing anions.
One known class of ionizing activator used in the production of propylene copolymers is fluorophenylborates and, in particular, perfluorophenylborates, the use of which is reviewed by Eugene at al. in Chem. Rev. 2000, 100, page 1391. Tetrakis(perfluoronaphthyl)borates have been shown to activate metallocene catalysts in a similar manner to their perfluorophenyl counterparts but yield copolymers with higher molecular weight under similar conditions using the same metallocene, the same reaction temperature, and the same conversion. However, tetrakis(perfluoronaphthyl)borates are harder to make and have higher raw material costs than the perfluorophenyl compounds. It would therefore be desirable to find an activator that has equivalent or better activity and molecular weight capabilities than tetrakis(perfluoronaphthyl)borate but is simpler and less expensive to produce.
According to the invention, it has now been found that certain mixed fluorophenyl/fluoronaphthylborates are effective activators for use with organometallic catalyst precursors in the polymerization of olefins, particularly of propylene with ethylene and higher alpha-olefins and can produce copolymers with molecular weights approaching those obtained with tetrakis(perfluoronaphthyl)borate activators.
U.S. Pat. No. 6,486,088 describes catalyst activators for asymmetrically bridged hafnocene catalyst precursors and use of the resultant catalysts in olefin polymerization, particularly the production of ethylene copolymers. The activators comprise a stable carbenium ion and a compatible non-coordinating anion, such as a halogenated tetraphenyl or tetranaphthyl boron compound. Suitable activators are said to include tropillium tetrakis(perfluoronapthyl) or tetrakis(perfluoro-4-biphenyl)borate, triphenylmethylium tetrakis(perfluoronapthyl) or tetrakis(perfluoro-4-biphenyl)borate, benzene(diazonium)tetrakis(perfluoronapthyl) or tetrakis(perfluoro-4-biphenyl)borate, tropillium tetrakis(perfluoronapthyl) or tetrakis(perfluoro-4-biphenyl)borate, triphenylnethylium tetrakis(perfluoronapthyl) or tetrakis(perfluoro-4-biphenyl)borate, benzene(diazonium)tetrakis(perfluoronapthyl) or tetrakis(perfluoro-4-biphenyl)orate, tropillium tetrakis(perfluoronapthyl) or tetrakis(perfluoro-4-biphenyl)borate, triphenylmethylium tetrakis(perfluoronapthyl) or tetrakis(perfluoro-4-biphenyl)borate, and benzene(diazonium) tetrakis(perfluoronapthyl) or tetrakis(perfluoro-4-biphenyl)borate. Anions with mixed ligands, such as tris(perfluorophenyl)(perfluoronapthyl)borate, are also said to be suitable, but no directions are provided as to how to synthesize such materials.
U.S. Pat. No. 6,559,253 describes a polymerization process for producing ethylene copolymers having a density of about 0.87 to about 0.930 comprising contacting, under homogeneous polymerization conditions at a reaction temperature of 140° C. to 220° C., ethylene and one or more comonomers capable of insertion polymerization with a catalyst complex derived from a bridged biscyclopentadienyl hafnium organometallic compound and an activating cocatalyst comprising a halogenated tetraaryl-substituted Group 13 anion wherein each aryl substituent contains at least two cyclic aromatic rings. Preferred anions are tetrakis(perfluoronapthyl)borates and tetrakis(perfluoro-4-biphenyl)borates. However, anions with mixed ligands, such as tris(perfluorophenyl)(perfluoroanthracyl)borate, are also referred to as being suitable, although again the reference is silent as to how to synthesize these mixed ligand anions.
U.S. Pat. No. 6,635,597 describes a catalyst activator adapted for use in the activation of metal complexes of metals of Group 3-10 for polymerization of ethylenically unsaturated polymerizable monomers, especially ethylene and propylene, comprising a neutral (Lewis acid) or charge separated (cation/anion pair) compound of the formula:(R1)r—B(Arf)m wherein B is boron; R1 independently each occurrence is a monovalent, anionic ligand group, with the proviso that for cationic compounds, one R1 additionally comprises a dissociated cation moiety; Arf independently each occurrence is a monovalent, fluorinated organic group containing from 10 to 100 non-hydrogen atoms, r is 0, 1, 2 or 3, and m is 1, 2 or 3; with the proviso that the sum of r and m is 3 or 4, and if r+m=3, then B is neutral and if r+m=4, then B is negatively charged, said charge being balanced by a cation component of one R1. Preferred and claimed examples of charge separated catalyst activators are said to include L+B−(C6F5)3(C10F7), L+B−(C6F5)2(C10F7)2, L+B−(C6F5)1(C10F7)3, and L30 B−(C10C7)4,wherein L+ is a cation of a Bronsted acid, ferrocenium, a carbonium cation, a silylium cation, Ag+, or the cationic derivative of a Group 3-10 metal complex catalyst. However, the reference fails to provide any information as to how to synthesize the mixed perfluorophenyl/perfluoronaphthyl compounds, with the only synthesis Examples being directed to the production of tris(β-perfluoronaphthyl)methyl boranes.